1. Field of the Invention
The present invention relates to a driven pulley structure forming part of a continuously-variable, V-belt-type power transmission. More particularly, the present invention relates to a variable width driven pulley structure, wherein the driven pulley includes an improved cam surface profile in which the separation between the pulley-engaging drive faces is controlled by a cam arrangement including a convex cam surface that provides improved performance for a vehicle in which a belt-type transmission utilizing the improved cam surface profile is installed.
2. Description of the Related Art
Continuously variable, V-belt-type power transmissions utilizing variable width drive and driven pulleys are well known. Such power transmissions are utilized on a wide variety of vehicles, including automobiles, utility vehicles, and golf carts, among others. The transmissions provide a stepless transfer of power from an electric motor or a gasoline engine to a driven output shaft that is operatively connected with one or more drive wheels of the vehicle. Additionally, such transmissions provide an advantage when applied to vehicles in that they respond automatically to changing load requirements by sensing the need for changes in input torque to the driving wheels. For example, when a vehicle is proceeding uphill and additional torque is required to maintain speed, the necessary increase in transmission output torque operates to increase the pull of the drive belt on the driven pulley, causing the faces of the driven pulley to move toward each other, to thereby increase the effective drive radius of the driven pulley and to decrease the effective drive radius of the driving pulley, as a result of which the torque at the transmission output shaft is increased.
Several patents disclose the provision of a cam and cam follower arrangement to govern the rate of movement of the pulley faces toward and away from each other in response to the torque demands placed upon the pulley structure. For example, in U.S. Pat. No. 3,722,308, which issued on Mar. 27, 1973, to Herbert Steuer, there is disclosed a variable spacing pulley in which a generally circular cam element is provided that has a concave cam surface that curves gradually in the axial direction of the pulley.
In U.S. Pat. No. 4,173,155, which issued on Nov. 6, 1979, to Paul G. Togami, et al., shows a torque sensing drive in which a two lobe, circular cam member is provided, wherein the cam surfaces between the cam lobes are defined by concave, generally parabolic curves.
In U.S. Pat. No. 4,826,467, which issued on May 2, 1989, to Terry L. Reese, et al., and which is assigned to the assignee of the present application, a variable spacing pulley structure is disclosed in which a circular cam surface having three cam lobes is disclosed. The cam surfaces are defined by triangular cam lobes in the form of helical surfaces that have a constant angular pitch, which when viewed in two-dimensional, developed form are straight lines. That cam surface configuration has been found to be generally acceptable and has been used in commercially available golf cars, utility vehicles, and the like. However, at times the engine that powers such vehicles will tend to overspeed on initial acceleration, and the shift into a higher torque mode during hill climbing is less abrupt than is desired.
Other patents that disclose such pulleys having flat, rectilinear cam surfaces include U.S. Pat. Nos. 4,403,976; 4,523,917; 4,585,429; and 4,592,737.
It is an object of the present invention to provide an improved cam profile to provide smoother operation and to avoid engine overspeed upon initial acceleration.
It is another object of the present invention to provide an improved cam profile to provide improved hill-climbing performance in a vehicle incorporating such a transmission arrangement.